Oh, we've been down this road many times before. Our house is old, built in the 50's and then added on to throughout the years. From the moment we moved in, we started having trouble with cooling, but, it wasn't that bad, so we just dealt with it. Then we were told that our DD needed a second hip surgery, the first resulted in a full body cast that she wore for 5 months. So we scrambled to try and get that house cold so that she'd be a little more comfy. New larger unit, new ductwork and 8K later, it was tolerable but never 'cold'. Thankfully, she wasn't in a cast after the surgery.
I'm just glad that, even though 500 hurts, it's not as bad as it could have been. I just spoke to the guy, and everything is working perfectly, no additional charge. However, after we've recovered from the trip, I'm going to schedule a complete duct inspection.